Netty: Why different packets are connected together as an request in the server?

Question

Here's the only handler in the Netty client, I sent 3 packets to the server.

@Sharable
public class ClientHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelActive(ChannelHandlerContext ctx) {
        ctx.writeAndFlush(Unpooled.copiedBuffer("1", CharsetUtil.UTF_8));
        ctx.writeAndFlush(Unpooled.copiedBuffer("2", CharsetUtil.UTF_8));
        ctx.writeAndFlush(Unpooled.copiedBuffer("3", CharsetUtil.UTF_8))
                .addListener(ChannelFutureListener.CLOSE);
    }
}

In the server handler, I just print it, expected 3 times with separate 1 , 2 and 3 , but 123 actually. What happened? Isn't them different packets?

@Sharable
public class ServerHandler extends SimpleChannelInboundHandler<ByteBuf> {
    @Override
    public void channelRead0(ChannelHandlerContext ctx, ByteBuf in) {
        System.out.println(in.toString(CharsetUtil.UTF_8));
    }
}

Answer 1

TCP/IP protocol (that you are probably using in your server) is stream-based. That means the buffer of a stream-based transport is not a queue of packets but a queue of bytes. So it is up to OS how to send your data - as separate packets or as 1 packet with all your data combined.

You have 3 options either add some separator or send fixed length packets or attach packet size to message.

Here is more details in netty documentation.